This invention relates to method of oxidizing cyclohexane to adipic acid and more specifically, how to remove catalyst as a solution after the reaction, preferably for recycling.
There is a plethora of references (both patents and literature articles) dealing with the formation of acids, one of the most important being adipic acid, by oxidation of hydrocarbons. Adipic acid is used to produce Nylon 66 fibers and resins, polyesters, polyurethanes, and miscellaneous other compounds.
There are different processes of manufacturing adipic acid. The conventional process involves a first step of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclohexanol (KA mixture), and the oxidation of the KA mixture with nitric acid to adipic acid. Other processes include, among others, the xe2x80x9cHydroperoxide Process,xe2x80x9d the xe2x80x9cBoric Acid Process,xe2x80x9d and xe2x80x9cDirect Synthesis Process,xe2x80x9d which involves direct oxidation of cyclonexane to adipic acid with oxygen in the presence of solvents, catalysts, and promoters.
The Direct Synthesis Process has been given attention for a long time. However, to this date it has found little commercial success. One of the reasons is that although it looks very simple at first glance, it is extremely complex in reality. Due to this complexity, one can find strikingly conflicting results, comments, and views in different references.
It is well known that after a reaction has taken place according to the Direct Synthesis, a mixture of two liquid phases is present at ambient temperature, along with a solid phase mainly consisting of adipic acid. The two liquid phases have been called the xe2x80x9cPolarxe2x80x9d phase and the xe2x80x9cNon-Polarxe2x80x9d or xe2x80x9cApolarxe2x80x9d phase. However, no attention has been paid so far to the importance of the two phases, except for separating the adipic from the xe2x80x9cPolarxe2x80x9d phase and recycling these phases to the reactor partially or totally with or without further treatment.
In more general nomenclature of phases, xe2x80x9cpolar phasexe2x80x9d is the more polar phase, while xe2x80x9cnon-polarxe2x80x9d or xe2x80x9capolarxe2x80x9d phase is the less polar phase.
It is also important to note that most studies on the Direct Synthesis have been conducted in a batch mode, literally or for all practical purposes.
As aforementioned, there is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid and/or intermediate products, such as for example cyclohexanone, cyclohexanol, cyclohexylhydroperoxide, etc.
The following references, among others, may be considered as representative of oxidation processes relative to the preparation of diacids and other intermediate oxidation products.
U.S. Pat. No. 5,463,119 (Kollar) discloses a process for the oxidative preparation of C5-C8 aliphatic dibasic acids by
(1) reacting,
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and
(b) an excess of oxygen gas or an oxygen-containing gas in the presence of
(c) a solvent comprising an organic acid containing only primary and/or secondary hydrogen atoms and
(d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst;
(2) removing the aliphatic dibasic acid; and
(3) recycling intermediates, post oxidation components, and derivatives thereof remaining after removal of the aliphatic dibasic acid into the oxidation reaction.
U.S. Pat. No. 5,374,767 (Drinkard et al.) discloses formation of cyclohexyladipates in a staged reactor, e.g., a reactive distillation column. A mixture containing a major amount of benzene and a minor amount of cyclohexene is fed to the lower portion of the reaction zone and adipic acid is fed to the upper portion of the reaction zone, cyclohexyladipates are formed and removed from the lower portion of the reaction zone and benzene is removed from the upper portion of the reaction zone. The reaction zone also contains an acid catalyst.
U.S. Pat. No. 5,321,157 (Kollar) discloses a process for the preparation of C5-C8 aliphatic dibasic acids through oxidation of corresponding saturated cycloaliphatic hydrocarbons by
(1) reacting, at a cycloaliphatic hydrocarbon conversion level of between about 7% and about 30%,
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and
(b) an excess of oxygen gas or an oxygen containing gas mixture in the presence of
(c) less than 1.5 moles of a solvent per mole of cycloaliphatic hydrocarbon (a), wherein said solvent comprises an organic acid containing only primary and/or secondary hydrogen atoms and
(d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; and
(2) isolating the C5-C8 aliphatic dibasic acid.
U.S. Pat. No. 3,987,100 (Barnette et al.) describes a process of oxidizing cyclohexane to produce cyclohexanone and cyclohexanol, said process comprising contacting a stream of liquid cyclohexane with oxygen in each of at least three successive oxidation stages by introducing into each stage a mixture of gases comprising molecular oxygen and an inert gas.
U.S. Pat. No. 3,957,876 (Rapoport et al.) describes a process for the preparation of cyclohexyl hydroperoxide substantially free of other peroxides by oxidation of cyclohexane containing a cyclohexane soluble cobalt salt in a zoned oxidation process in which an oxygen containing gas is fed to each zone in the oxidation section in an amount in excess of that which will react under the conditions of that zone.
U.S. Pat. No. 3,932,513 (Russell) discloses the oxidation of cyclohexane with molecular oxygen in a series of reaction zones, with vaporization of cyclohexane from the last reactor effluent and parallel distribution of this cyclohexane vapor among the series of reaction zones.
U.S. Pat. No. 3,530,185 (Pugi) discloses a process for manufacturing precursors of adipic acid by oxidation with an oxygen-containing inert gas which process is conducted in at least three successive oxidation stages by passing a stream of liquid cyclohexane maintained at a temperature in the range of 140xc2x0 C. to 200xc2x0 C. and a pressure in the range of 50 to 350 p.s.i.g. through each successive oxidation stage and by introducing a mixture of gases containing oxygen in each oxidation stage in an amount such that substantially all of the oxygen introduced into each stage is consumed in that stage thereafter causing the residual inert gases to pass countercurrent into the stream of liquid during the passage of the stream through said stages.
U.S. Pat. No. 3,515,751 (Oberster et al.) discloses a process for the production of epsilon-hydroxycaproic acid in which cyclohexane is oxidized by liquid phase air oxidation in the presence of a catalytic amount of a lower aliphatic carboxylic acid and a catalytic amount of a peroxide under certain reaction conditions so that most of the oxidation products are found in a second, heavy liquid layer, and are directed to the production of epsilon-hydroxycaproic acid.
U.S. Pat. No. 3,361,806 (Lidov et al.) discloses a process for the production of adipic acid by the further oxidation of the products of oxidation of cyclohexane after separation of cyclohexane from the oxidation mixture, and more particularly to stage wise oxidation of the cyclohexane to give high yields of adipic acid precursors and also to provide a low enough concentration of oxygen in the vent gas so that the latter is not a combustible mixture.
U.S. Pat. No. 3,234,271 (Barker et al.) discloses a process for the production of adipic acid by the two-step oxidation of cyclohexane with oxygen. In a preferred embodiment, mixtures comprising cyclohexanone and cyclohexanol are oxidized. In another embodiment, the process involves the production of adipic acid from cyclohexane by oxidation thereof, separation of cyclohexane from the oxidation mixture and recycle thereof, and further oxidation of the other products of oxidation.
U.S. Pat. No. 3,231,608 (Kollar) discloses a process for the preparation of aliphatic dibasic acids from saturated cyclic hydrocarbons having from 4 to 8 cyclic carbon atoms per molecule in the presence of a solvent which comprises an aliphatic monobasic acid which contains only primary and secondary hydrogen atoms and a catalyst comprising a cobalt salt of an organic acid, and in which process the molar ratio of said solvent to said saturated cyclic hydrocarbon is between 1.5:1 and 7:1, and in which process the molar ratio of said catalyst to said saturated cyclic hydrocarbon is at least 5 millimoles per mole.
U.S. Pat. No. 3,161,603 (Leyshon et al.) discloses a process for recovering the copper-vanadium catalyst from the waste liquors obtained in the manufacture of adipic acid by the nitric acid oxidation of cyclohexanol and/or cyclohexanone.
U.S. Pat. No. 2,565,087 (Porter et al.) discloses the oxidation of cycloaliphatic hydrocarbons in the liquid phase with a gas containing molecular oxygen and in the presence of about 10% water to produce two phases and avoid formation of esters.
U.S. Pat. No. 2,557,282 (Hamblet et al.) discloses production of adipic acid and related aliphatic dibasic acids; more particularly to the production of adipic acid by the direct oxidation of cyclohexane.
U.S. Pat. No. 2,439,513 (Hamblet et al.) discloses the production of adipic acid and related aliphatic dibasic acids and more particularly to the production of adipic acid by the oxidation of cyclohexane.
U.S. Pat. No. 2,223,494 (Loder et al.) discloses the oxidation of cyclic saturated hydrocarbons and more particularly to the production of cyclic alcohols and cyclic ketones by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
U.S. Pat. No. 2,223,493 (Loder et al.) discloses the production of aliphatic dibasic acids and more particularly to the production of aliphatic dibasic acids by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
German Patent DE 44 26 132 A1 (Kysela et al.) discloses a method of dehydration of process acetic acid from liquid-phase oxidation of cyclohexane with air, in the presence of cobalt salts as a catalyst after separation of the adipic acid after filtration, while simultaneously avoiding cobalt salt precipitates in the dehydration column, characterized in that the acetic acid phase to be returned to the beginning of the process is subjected to azeotropic distillation by the use of added cyclohexane, under distillative removal of the water down to a residual content of less than [sic] 0.3-0.7%.
PCT International Publication WO 96/03365 and U.S. Pat. No. 5,756,837 (both of Costantini et al.) disclose a process for recycling a cobalt-containing catalyst in a direct reaction of oxidation of cyclohexane into adipic acid, characterized by including a step in which the reaction mixture obtained by oxidation into adipic acid is treated by extraction of at least a portion of the glutaric acid and the succinic acid formed during the reaction.
German Patent Publication DE 44 27 474 A1 (Ohst et al.) discloses a method consisting of cooling the reaction mixture, separating the precipitated adipic acid by filtration, separating the filtrate into a polar and a non-polar phase, a portion of which polar phase is extracted, and the catalyst present in this portion is recovered (a) by mixing with cyclohexanone, followed by removal by distillation of the acetic acid present and filtration; or (b) by removal by distillation of the majority of the acetic acid present, hydrolytic decomposition of the distillation residue, and extraction in the form of an aqueous solution of the organic constituents then present with the exception of the catalyst. None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, control of oxidation reactions subject to the intricate and critical controls and requirements of the instant invention as described and claimed.
Our U.S. Pat. Nos. 5,654,475, 5,580,531, 5,558,842, 5,502,245, 5,801,282, and co-pending application Ser. No. 08/587,967, filed on Jan. 17, 1996, all of which are incorporated herein by reference, describe methods and apparatuses relative to controlling reactions in atomized liquids. In addition, our U.S. Pat. Nos. 5,801,273 and 5,817,868, and the following co-pending U.S. applications are also incorporated herein by reference: Ser. No. 08/812,847, filed on Mar. 6, 1997; Ser. No. 08/824,992, filed on Mar. 27, 1997; Ser. No. 08/861,281 filed on May 21, 1997; Ser. No. 08/861,180 filed on May 21, 1997; Ser. No. 08/861,176 filed on May 21, 1997; Ser. No. 08/861,210 filed on May 21, 1997; Ser. No. 08/876,692, filed on Jun. 16, 1997; Ser. No. 08/900,323, filed on Jul. 25, 1997; Ser. No. 08/931,035, filed on Sep. 16, 1997; Ser. No. 08/932,875 filed on Sep. 18, 1997; Ser. No. 08/934,253, filed on Sep. 19, 1997; Ser. No. 08/986,505, filed on Dec. 8, 1997; Ser. No. 08/989,910, filed on Dec. 12, 1997; No. 60/074,068, filed on Feb. 9, 1998; No. 60/075,257, filed Feb. 19, 1998; No. 60/086,159, filed May 20, 1998; No. 60/086,119, filed May 20, 1998; No. 60/086,118, filed May 20, 1998; No. 60/091,483, filed on Jul. 2, 1998.
As aforementioned, this invention relates to methods of oxidizing hydrocarbons, such as cyclohexane for example, to respective intermediate oxidation products, such as adipic acid for example, and more specifically, how to remove catalyst in solution after the reaction, preferably for recycling. More particularly, this invention pertains a method of treating a reaction mixture produced by direct oxidation of cyclohexane to adipic acid, the reaction mixture comprising cyclohexane, adipic acid, a monobasic acid solvent having only primary and/or secondary hydrogen atoms, optionally water, and a metal ion catalyst, the method being characterized by steps of:
(a) removing substantially the totality of the cyclohexane;
(b) removing a major part of the adipic acid;
(c) removing substantially the totality of the monobasic acid solvent by distillation, during which a protic solvent is added continuously or intermittently in an adequate amount substantially to prevent solids precipitation, to provide a first single liquid phase, the first single liquid phase being homogeneous and solids-free, the protic solvent containing no carboxylic or mineral acid groups and having a normalized solvent polarity parameter EN in the range of 0.9 to 1.0;
(d) adding to the first single liquid phase a dipolar aprotic solvent and, if needed, additional protic solvent, in such quantities so as to provide a second single liquid phase that is homogeneous and solids-free at a desired first temperature, the dipolar aprotic solvent having a normalized solvent polarity parameter EN in the range of 0.2 to 0.4;
(e) causing formation of two liquid phases, a solids-free protic liquid phase containing substantially all the metal ion catalyst, and a solids-free aprotic liquid phase containing at least the majority of ingredients of the reaction mixture, by a process selected from a group consisting of lowering the first temperature to a second temperature, adding additional protic solvent, adding an apolar aprotic solvent having a EN value in the range of 0.0 to 0.1, and a combination thereof; and
(f) separating the solids-free protic liquid phase containing the catalyst from the solids-free aprotic liquid phase; wherein EN is defined by equation (1)                               E          N                =                                                                              E                  T                                ⁡                                  (                  solvent                  )                                            -                                                E                  T                                ⁡                                  (                  TMS                  )                                                                                                      E                  T                                ⁡                                  (                  water                  )                                            -                                                E                  T                                ⁡                                  (                  TMS                  )                                                              =                                                                      E                  T                                ⁡                                  (                  solvent                  )                                            -              30.7                        32.4                                              (        1        )            
using water and tetramethylsilane as extreme reference solvents, such that ET(solvent) is the ET value corresponding to the solvent under consideration, ET(TMS) is the ET value corresponding to tetramethylsilane, and ET(water) is the ET value corresponding to water,
and wherein ET is defined by equation (2)
ET/(kcalxc2x7molxe2x88x921)=hxc2x7cxc2x7vxc2x7NA=2.859xc3x9710xe2x88x923xc2x7v/cmxe2x88x921xe2x80x83xe2x80x83(2)
in which v is the wavenumber (cmxe2x88x921) of the photon which produces the electronic excitation, h is Plank""s constant, c is the velocity of light, and NA is Avogadro""s Number, ET being based either directly on the transition energy for the longest wavelength solvatochromic absorption band of pyridinium-N-phenoxide betaine dye in the solvent under consideration, or indirectly by the use of the more lipophilic penta-tert-butyl-substituted pyridinium-N-phenoxide betaine dye in the solvent under consideration.
Further, the present invention is related to a method of separating catalyst in a solution form from a reaction mixture produced by direct oxidation of cyclohexane to adipic acid, the reaction mixture comprising cyclohexane, adipic acid, a monobasic acid solvent having only primary and/or secondary hydrogen atoms, optionally water, and a metal ion catalyst, the method being characterized by steps of:
(a) removing substantially the totality of the cyclohexane;
(b) optionally removing a major part of the adipic acid;
(c) forming a first solids-free single liquid phase containing less than about 20% by weight monobasic acid solvent by removing an adequate amount of said monobasic acid solvent;
(d) adding, to the first single liquid phase, a dipolar aprotic solvent and, if needed, additional protic solvent, in such quantities so as to provide a second single liquid phase that is homogeneous and solids-free at a desired first temperature, the dipolar aprotic solvent having a normalized solvent polarity parameter EN in the range of 0.2 to 0.4;
(e) causing formation of two liquid phases, a solids-free protic liquid phase containing substantially all the metal ion catalyst, and a solids-free aprotic liquid phase containing at least the majority of ingredients of the reaction mixture by a process selected from a group consisting of lowering the first temperature to a second temperature, adding additional protic solvent, adding an apolar aprotic solvent having a EN value in the range of 0.0 to 0.1, and a combination thereof; and
(f) separating the solids-free protic liquid phase containing the catalyst from the solids-free aprotic liquid phase;
The weight ratio of the first single liquid phase to the total protic solvent used in steps (c), and (d), is preferably in the range of 1 to 3. Also, the weight ratio of the dipolar aprotic solvent used in steps (c) and (d) to the first single liquid phase is preferably in the range of 1 to 3.
The first temperature is preferably in the range of 80 to 120xc2x0 C., and more preferably in the range of 90 to 110xc2x0 C., while the second temperature is in the range of preferably 15 to 50xc2x0 C., more preferably 20 to 40xc2x0 C., and even more preferably 20 to 30xc2x0 C.
Steps (a) and (b) preferably precede steps (c), (d), (e), and (f).
The method may further comprise a step of recycling the solids-free protic liquid phase to a reaction zone, in which reaction zone cyclohexane is oxidized to adipic acid, either directly or indirectly, and/or with or without removal of protic solvent, and/or with or without addition of monobasic acid solvent.
The method may also comprise a step of hydrolyzing esters contained in the solids-free aprotic liquid phase.
The methods of this invention are particularly applicable in the case that the monobasic acid solvent comprises acetic acid, the protic solvent comprises water, the metal ion catalyst comprises cobalt ions, the dipolar aprotic solvent comprises cyclohexanone, and the apolar aprotic solvent comprises cyclohexane.
The methods of the invention may further comprise a step of reacting the adipic acid with a reactant selected from a group consisting of a polyol, a polyamine, and a polyamide in a manner to form a polymer of a polyester, or a polyamide, or a (polyimide and/or polyamideimide), respectively. In addition, the method may also comprise a step of spinning the polymer into fibers, and/or adding to the polymer fillers and/or other additives to form composites.